The invention relates to a method for desanding or removing sand from castings cast in moulding sand by means of at least one fluid pressure pulse acting on the sand mould.
In modern foundry technology the manufacture of the sand mould for box-linked or boxless casting and the subsequent casting has been improved to a high technological state. However, this does not apply with respect to the finishing of the castings, particularly the preliminary desanding and desanding of the castings. To the extent that these are mechanical processes, the mould body, optionally together with the mould box, is vibrated, rolled or pounded, which is on the one hand associated with relatively high energy costs and on the other with considerable noise emission. In addition, the order state of the castings in the mould body is broken up and the castings pass into uncontrolled positions, which through the feeder and riser present at the casting extend to complicated confused layers. It is then virtually impossible to handle them with automated equipment, so that manual action is necessary. In addition, in areas where the moulding sand has been removed from them, the castings are directly exposed to the mechanical forces and are consequently often damaged. This more particularly applies during desanding on deflecting grates, vibrating conveyors or in cooling drums.
Therefore numerous attempts have been made to substitute these mechanical desanding processes and in particular to reduce or completely avoid noise and dust emissions. Thus, inter alia, preliminary desanding by pressurized water is known, which substantially avoids noise and dust emissions. However, the considerable water requirement and the treatment of the water required by water regulations make this problematical. In addition, temperature and stress cracks can occur on the casting. These problems are avoided when desanding by compressed air pulses (DE-journal "Giesserei-technik" 1998, p 37). This method uses the same principle as for moulding machines for the manufacture of the mould. In this method hitherto only known for box casting, a hood is placed on the moulding box and by means of a rapidly opening valve a large-area compressed air blast is applied to the sand surface. This known method functions with relatively lower energy costs and reduced noise emission, whilst at the same time protecting the castings. However, this method has not hitherto been successful in practice, because the casting is only inadequately desanded.